As an absorbent resin particle excellent in absorption rate, there is known an absorbent resin particle having a structure wherein a hydrophobic substance is contained in the inside of a crosslinked polymer (Patent Document 1).
Also, there is known an absorbent resin particle wherein powder flowability and the like are improved by attaching a hydrophobic substance on the surface of a crosslinked polymer (Patent Document 2).
However, in the conventional absorbent resin particles and water absorbers, an absorption rate with the passage of time after they come into contact with a liquid to be absorbed (hereinafter referred to as absorption rate pattern) is not appropriate. Specifically, the conventional absorbent resin particles include an absorbent resin particle (i) having an absorption rate pattern where the rate is fast in the early stage, moderate in the middle stage, and moderate in the late stage (the above mentioned absorbent resin particle of Patent Document 1) and an absorbent resin particle (ii) having an absorption rate pattern where the rate is slow in the early stage, moderate in the middle stage, and moderate in the late stage (the above-described absorbent resin particle of Patent Document 2).
When these absorbent resin particles are applied to absorbent articles (disposable diapers, etc.), in the absorbers used in the absorbent articles, absorption ratios of the absorbent resins become uneven depending on the portions of the absorbers and thus the absorbers cannot be effectively used, so that there tends to arise problems that portions on which the liquid to be absorbed remains are apt to occur or time during which the liquid not absorbed all over the absorber stays is prolonged.
Specifically, in the case where the above-described absorbent resin particle (i) is used, a liquid to be adsorbed is rapidly absorbed in the initial stage after the contact with the absorbent resin particle at the portions with which the liquid comes into contact. However, when the absorbent resin particle absorbs the liquid and swells to become a gel form, diffusion and absorption of unabsorbed liquid is prevented and, as a result, there occurs unevenness in the absorption ratio that the absorption ratio of the absorbent resin particle is high at the portions which come into contact with the liquid to be absorbed and the absorption ratio of the absorbent resin particle is low at peripheral portions thereof. Thus, at the portions which come into contact with the liquid to be absorbed, the liquid not absorbed is apt to remain.
On the other hand, in the case where the above-described absorbent resin particle (ii) is used, the liquid is only gradually absorbed after the contact with the absorbent resin particle at the portions with which the liquid to be adsorbed comes into contact and unabsorbed liquid diffuses into the inside of the absorber. As a result, the absorption ratio of the absorbent resin particle tends to be equal at the portions with which the liquid to be absorbed comes into contact and at peripheral portion thereof. However, since the absorption rate is wholly slow, the time during which the liquid not absorbed all over the absorber stays is prolonged.
In these absorbent resin particles, at the portions where the unabsorbed liquid remains or at the portions where the liquid stays for a long time, there is a problem that a trouble such as skin irritation tends to occur on the skin of a wearer who comes into contact with the portions.